Using a Map and Compass

March 10, 2011 @ 8:18pm

The compass is a great tool to use when navigating through wilderness areas. Due to the north/south needle being magnetised, this needle automatically aligns itself to Earth’s magnetic field. The north (red) end of the needle always points to the magnetic North pole. Magnetic north is approximately 1300 km south of the geographic North Pole (True North) and varies in location over time. In Canada, just west of Thunder Bay, close to the town of Atikokan magnetic north and true north point in the same direction (0 degrees). As you move west or east from this point (prime meridian) there is an increasing angle of difference between true north and magnetic north. This phenomenon is often referred to as declination. If you were living on the Queen Charlotte Islands in British Columbia, the declination would be 25 degrees EAST. The compass needle would point 25 degrees from true north in an easterly direction. Likewise, if you were in Atlantic Canada in Labrador, the declination would be 25 degrees WEST. The compass need would point 25 degrees from true north in a westerly direction. All topographic maps are oriented with true (geographic) north at the top of the map sheet. When using a map when travelling in the bush you must incorporate the declination to ensure you are heading in the right direction. Most compasses have a tiny little screw that when turned sets the declination for the area that you are in. Declination information is found on the edge of each topographic map sheet. If this screw feature is not available on your compass, you must remember the saying, “WEST is BEST” and “EAST is LEAST”. To clarify, in Labrador, since the magnetic north is WEST of your location, you would ADD 25 degrees to you compass reading. Likewise, in the Queen Charlottes, since magnetic north is EAST of your location you would SUBTRACT 25 degrees from your compass reading. In Sault Ste. Marie the declination is approximately 7 degrees WEST.

When planning a route on a map, place the flat edge of the compass at your starting point and ending point with the black arrow pointing in the direction you will be traveling. Disregard what the magnetic needle is doing. On the circular housing you will notice parallel red or black lines. Turn the housing until these lines line-up with the north/south grid lines on the map. On the compass, now read the direction you will be travelling in degrees. Remember, if you have not preset your declination in the compass housing, you will have to add or subtract the declination from the reading you have acquired.

In the field, set the direction you are travelling in degrees. Many compasses come with a mirror with a sighting device. This aids in following a bearing you have set. Holding the compass flat – parallel to the ground, rotate you body until the red north needle and the red north guide arrow inside the housing line up. Slightly lower the mirror until you can see the top of the compass in the mirror. With the north needle aligned with the guide arrow you will be travelling in the direction. On the case surrounding the mirror you will notice a v shaped notch. Look through this notch and pick a distant object. Lower the compass and walk to that object. Once there pick up the compass set it up again to the needle and guide arrow line up and pick another distant object to walk towards. At this point repeat until you reach your destination. Congratulations, you have successfully mastered using a map and compass.

It should be noted that at times a compass may give false readings. This is largely due to magnetic ore deposits on the earth’s surface. Magnetic Point in vicinity of Silver Islet area close to Thunder Bay is noted for wrecking havoc with compasses. The compass needle may spin or be wildly offset from the bearing you are trying to maintain due to the interference of the ore body. As you move away from the interference, the compass will return to aligning itself with the magnetic lines of the Earth. Also, it is good to keep in mind that any metal material or electronics close to the compass will skew its reading. As you approach the North Pole the compass will lose its effectiveness due to the closeness of magnetic lines. It will begin to drift and the needle may point up and down and get stuck. That is why Inuit do not use compasses in the far north.

If you are looking for a compass, Joe Sport & Surplus stocks various models. Come in and talk to us. We will help you with your route into wilderness.

Check out our Global Suunto Compass. Read the information below related to the benefits of a Global Needle/ Global Compass

Before you can fully understand a "Global Needle", you must understand a few basic principles of a compass.

In order to get an accurate reading from a compass, the compass needle needs to be "balanced" in the capsule, so it does not drag on the top or bottom of the capsule. But, because the horizontal and vertical components of the earth's magnetic field vary considerably in different locations, a compass needle that "balances" perfectly in New Zealand will drag or stick in Europe or North America for example.

As a result of these magnetic variances, the compass industry has divided the earth into 5 "zones", as identified in the map which shows the different zones starting with Zone 1 at the top and ending with Zone 5 at the bottom (Australia and New Zealand only). All of the standard compasses sold at New Zealand are balanced for Zone 5.A typical feature for regular compasses is that they can function without problems only at limited longitudes because the changes in the magnetic field affect the position of the needle. For fast needles, this phenomenon is even more prominent.

In the global compass, this problem has been solved with a structural innovation. The needle and magnet are built as separate units functioning independently from each other, so that the inclination of the magnetic field cannot tilt the needle. The needle can no longer move vertically. It is the compass magnet, separated from the needle, which absorbs the vertical force of the magnetic field. The needle itself is fixed at the lid by means of a double jeweled bearing. The magnet rotates with its jewel bearing on a pin. Such a compass works reliably in all zones of the world. Due to the strong magnet, the needle settles very quickly and stops immediately at the right position, allowing for an extremely accurate reading.

In addition, the global needle's unique ability to handle tilts up to 20 degrees makes it perfect for trampers who don't want to break their stride. Not having to level the compass exactly makes it easier to take an accurate reading while you're still moving along the track.